Patent Literature 1 discloses a pump that draws fuel into a gear housing chamber and discharges the fuel. The pump includes: an outer gear having inner teeth; an inner gear having outer teeth and meshing with the outer gear in eccentric state; and a pump housing that defines a cylindrical gear housing chamber housing the outer gear and the inner gear to be rotatable from both sides in the axial direction. The outer gear and the inner gear rotate, while expanding and contracting a volume of a pump chamber formed plurally between the outer gear and the inner gear, to sequentially draw fluid into and discharge from each of the pump chambers.
The pump housing has a spiral-shaped groove formed from a radially-inside corner part opposing a radially-outside corner part of the outer gear toward a central part.